The present invention relates to piston rings and more particularly to a piston ring joint or gap defined by the ends of a parted, annular piston ring body.
Heretofore, various proposals have been made for piston rings having a parted, annular body and defining an overlapping joint structure for sealing high pressure fluids from one or from either side. Piston rings of this type have found utility in diesel engines involving high compression ratios. The overlapping joint constructions attempt to reduce the blow-by or leakage past the rings in such applications. Bi-directional ring joints have also found utility in various forms of hydraulic equipment such as double or single acting rams and in high pressure compressors.
The piston rings of the type under consideration are received within compression ring grooves of the piston and define a sealing surface which bears against the cylinder wall and a sealing surface which bears on the bottom ring groove side. The resilience of the piston ring initially forces the ring into contact with the cylinder wall. Fluid under pressure acting on one of the sides of the piston ring may leak past the piston ring side and down the inner circumferential face of the ring into the piston ring groove and then through the joint. It may also leak axially of the piston through the ring part. The leakage problem is aggravated by the fact that the joint structure must be constructed to provide sufficient clearance for thermal expansion and to compensate for cylinder tolerances.
One form of high pressure compression ring which has heretofore been proposed includes a pair of projections extending circumferentially from the ends of the ring body. Each projection defines an angled sealing surface with the sealing surfaces being oppositely related so as to mate when the gap is closed and the projections are overlapped to define the joint. In this type of seal ring, the high pressure side projection of the joint may be pentagonal or triangular and the lower or bottom side projection of the joint is triangular. In order to effectively seal in double acting piston installations, half of the rings of this type are usually installed with the pressure side facing in one direction and the other half of the rings are installed with the pressure side facing in the opposite direction.
Another form of high pressure sealing ring presently available includes a projection extending circumferentially adjacent the inner, circumferential face of one end of the ring and a projection extending circumferentially adjacent the outer, circumferential face of the other end of the ring. The ends of the ring define horizontally disposed or radially extending sealing surfaces which overlap when the gap is closed. This form of ring provides a sealing surface between the joint and the cylinder wall, between the bottom side of the ring and the bottom ring groove side and between the horizontal disposed sealing surfaces, one of which is defined by a projection and the other of which is defined by a recess formed in the ends of the ring.